Effects Of Biochar Application On Soil Fertility Of Pure Eucalyptus Grandis × E.urophylla Plantations And Its Mixed Plantations With Dalbergia Odorifera

Eucalyptus is one of the timber species with the largest planting area in the world.However,due to its pure forest cultivation mode,it is easy to cause problems such as the decline of site quality and plant diversity.Constructing the Eucalyptus mixed forest is the main measure to solve this problem.In this paper,pure Eucalyptus grandis x E.urophylla forest and mixed forest withe Dalbergia odorifera are taken as research objects,and biochar treatment was added to two different forests.There were four different treatment groups,namely pure forest control group(PCK),(Eucalyptus grandis x E.urophylla)x Dalbergia odorifera mixed forest control group(MCK),pure forest added biochar group(PCA)and mixed forest added biochar group(MCA).The soil physical?chemical properties,soil nutrients and soil microbial biomass of four different groups were measured.The differences in soil fertility between pure Eucalyptus forest and mixed Eucalyptus/Dalbergia odorifera forest after biochar input were discussed.The following conclusions were obtained:(1)Biochar input and construction of Eucalyptus/Dalbergia odorifera mixed forest can significantly reduce the topsoil bulk density,and make the soil loose.However,the soil bulk density of 30-50cm layer and soil pH value were less affected by planting mode and biochar addition,the difference was not significant.In general,the introduction of nitrogen-fixing tree species and the addiing biochar are beneficial to improve soil physical properties.(2)Biochar input can significantly increase the contents and reserves of the soil carbon and nitrogen,with the carbon and nitrogen reserves increased by 23.48%and 14.14%,which effectively improved the soil carbon and nitrogen stability of Eucalyptus plantations.The construction of Eucalyptus/Dalbergia odorifera mixed forest reduced the soil carbon storage,which the control group and the adding biochar treatment group decreased by 18.84%and12.20%.However,under the action of biochar input,the nitrogen storage of mixed forest soil is higher than that of pure forest by 50.34%.(3)The construction of Eucalyptus/Darlbergia odorifera mixed forest and the addition biochar reduced the pH of the soil,and the reduction was extremely small,only 2.22%?4.44%.The input of biochar could significantly increase the total nitrogen and hydrolyzed nitrogen content of the mixed Eucalyptus forest soil(increased by 111.88%),but the effect on pure forest was not significant.Adding biochar increased the total nitrogen and hydrolyzed nitrogen content of the soil,but the amount of the nitrogen-free nitrogen group was significantly reduced.The addition of biochar had little effect on the total phosphorus content of the soil,which significantly increased the available phosphorus content,while it reduced the total potassium and available potassium content.Mixing forest construction reduced soil phosphorus content but increased its potassium content.(4)The effect of biochar input on soil trace metal elements was differenrt,which significantly increased the effective copper and zinc content in soil,but significantly reduced the content of soil exchangeable calcium and magnesium.The treatment increased the content of soil exchangeable calcium,magnesium and available copper and zinc,and the difference was not significant.When the biochar was not added,the content of mixed forest exchangeable calcium,magnesium and available copper and zinc were reduced by 37.15%,20.06%,22.22%and 35.71%.(5)The construction of Eucalyptus/Dalbergia/Dalbergia odorifera mixed forest reduced the number of soil bacteria,fungi and actinomycetes,and also reduced carbon dioxide flux and nitrous oxide flux,but increased methane flux,the difference was not significant(p>0.05).The input of biochar significantly reduced the biomass of soil bacteria,fungi,actinomycetes and soil microbial biomass in Eucalyptus plantations,with a reduction of 12.28%-76.54%,and also significantly reduced the absorption rate of CH4.Bbut biochar input significantly accelerated the CO2 and N2O emission rates of eucalyptus plantations.It can be seen that the introduction of nitrogen-fixing tree species and the addition of biochar can improve the site conditions of Eucalyptus artificial forest by changing the physical and chemical properties of the soil and the number of microorganisms,and solve the negative problem of Eucalyptus pure forestt on the site conditions.